Rice (i.e., Oryza sativa) is recognized to be an important food crop in many parts of the world. However, heretofore rice production has not benefited to a substantial degree from heterosis or hybrid vigor made possible when different parental lines are cross-pollinated. For a number of reasons primarily related to the unique rice plant morphology, the controlled cross-pollination of rice plants has been difficult to achieve on a commercial scale.
Representative articles which discuss hybrid rice production are:
(1) "Hybrid Rice--Problems and Potentials", by J.W. Stansel and J.P. Craigmiles, Rice Journal, Vol 69, No. 5, Pages 14 to 15, and 46 (1966). PA0 (2) "Outlook for Hybrid Rice in the USA", by H.L. Carnahan, J.R. Erikson, S.T. Tseng, and J.N. Rutger, Rice Breeding, International Rice Research Institute, Laguna, Philippines, Pages 603 to 607 (1972). PA0 (3) "Outlook for Hybrid Rice in India", by M.S. Swaminathan, E.A. Siddig, and S.D. Sharma, Rice Breeding, International Rice Research Institute, Laguna, Philippines, Pages 609 to 613 (1972). PA0 (4) "Current Status and Future Prospects for Breeding Hybrid Rice and Wheat", S.S. Virmani and Jan B. Edwards, Advances in Agronomy. Vol. 36, Pages 145 to 214 (1983). PA0 (5) "A Concise Course in Hybrid Rice", by Long P. Yuan, Hunan Science and Technology Publishers, Hunan, China, Pages 1 to 168 (1985). PA0 (6) "Current Status of Hybrid Rice Research and Development", by L. P. Yuan and S. S. Virmani, International Symposium on Hybrid Rice, Changsha, Hunan, China, Pages 1 to 16 plus tables (1986). PA0 (a) growing in a planting area a population of (i) female fertile cytoplasmically male sterile rice plants having substantially fully exserted stigmas, panicles which are substantially fully exserted, flag leaves which in the absence of cutting generally extend upwardly to a lesser maximum height than the tips of the panicles whereby the panicles are well disposed to receive pollen from nearby plants and the disposition of the flag leaves below the tips of the panicles is attributable to recessive genes, and the ability to form seeds which are associated with a dominantly inherited genetic marker, and (ii) female fertile male fertile rice plants which are capable of restoring male fertility to the progeny of the cytoplasmically male sterile rice plants having generally long erect flag leaves attributable to dominant genes which generally extend upwardly to a greater maximum height than the tips of the panicles, and the ability to form seeds when self-pollinated which are associated with a recessively inherited genetic marker, PA0 (b) pollinating the population of rice plants whereby seeds are formed on the female fertile cytoplasmically male sterile rice plants (i) which are capable of growing male fertile F.sub.1 hybrid rice plants having long flag leaves which generally extend upwardly to a greater maximum height than the tips of the panicles whereby efficient photosynthesis can be accomplished, and seeds are formed on the female fertile male fertile rice plants (ii) as a result of self-pollination, PA0 (c) recovering seeds which have formed on the rice plants growing in the planting area, and PA0 (d) substantially separating on the basis of the genetic marker the seeds capable of growing male fertile F.sub.1 hybrid rice plants formed on the (i) plants from the seeds formed on the (ii) plants as a result of self-pollination.
In U.S. Pat. No. 4,305,225 to Long P. Yuan, techniques are disclosed for aiding the production of hybrid rice. For instance, the male sterile seed parent plants can be sprayed with a growth hormone (e.g., gibberellin) in order to cause the flower-bearing panicles to more fully emerge from the rice leaf sheath. Any portion of the panicle which does not emerge will be incapable of receiving pollen from the pollen parent and thereby diminishes the yield of seeds capable of forming F.sub.1 hybrid rice. The application of the growth hormone adds a significant expense to the overall process.
In U.S. Pat. No. 4,351,130 to J. Neil Rutger et al a rice hybridization process is disclosed wherein the male pollinator plants are recessively inherited tall plants.
In U.S. Pat. No. 3,842,538 to Zoltan Barabas is disclosed a hybrid seed production process wherein hybrid grains and pure grains are separated on the basis of color. Unlike wheat and similar grains, rice grains possess an outer hull which if removed will normally reduce their viability for planting purposes.
Heretofore, hybrid rice production has been carried out in the Peoples Republic of China using a highly labor intensive technique wherein the male and female rice parents are first seeded separately at different times in different beds, transplanted to different adjoining areas, monitored for growth on a weekly basis by observing the leaf count, the rate of growth is adjusted by water and fertilizer management, a growth hormone such as gibberellin is applied to the seed parent plants in order to cause the flower panicles to be more fully exserted out of the leaf sheath, the flag leaves of the seed parent plants are clipped, if wind currents are deficient pollen sometimes is transferred by hand through the movement of a rope across the planting area, and the seeds which are capable of forming F.sub.1 hybrid rice plants are selectively harvested.
It is an object of the present invention to provide an improved procedure for forming seeds capable of growing male fertile F.sub.1 hybrid rice plants which is capable of being readily implemented on a commercial scale.
It is an object of the present invention to provide an improved procedure for forming seeds capable of growing male fertile F.sub.1 hybrid rice plants which can be carried out on a relatively economical basis without the need for extensive hand labor.
It is an object of the present invention to provide an improved procedure for forming seeds capable of growing male fertile F.sub.1 hybrid rice plants which requires no clipping of flag leaves.
It is an object of the present invention to provide an improved procedure for forming seeds capable of growing male fertile F.sub.1 hybrid rice plants wherein the parent plants optionally may be grown in a substantially random population.
It is an object of the present invention to provide an improved procedure for forming seeds capable of growing male fertile F.sub.1 hybrid rice plants wherein in a preferred embodiment the parent plants are each provided with at least one distinctive vegetative marker which is useful to identify the presence and concentrations of the key plants.
It is an object of the present invention to provide an improved procedure for forming seeds capable of growing male fertile F.sub.1 hybrid rice plants wherein the seeds formed on the parent plants may be simply harvested in bulk, and the seeds capable of growing male fertile F.sub.1 hybrid rice plants subsequently substantially separated from the seeds formed on the male parent plants.
It is another object of the present invention to provide a substantially homogeneous assemblage of rice seeds which upon growth yields female fertile cytoplasmically male sterile rice plants possessing a combination of characteristics which renders them particularly suited for use as a seed parent for use in hybrid rice production.
It is a further object of the present invention to provide cytoplasmically male sterile rice plants which possess a combination of characteristics which renders them particularly suited for use as a seed parent in hybrid rice production.
These and other objects, as well as the scope, nature, and utilization of the claimed invention will be apparent to those skilled in the art from the following detailed description and appended claims.